bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical analysis of 16th to 19th century Limoges School ‘painted enamel’ objects in three museums of the Low Countries
Authors: Van der Linden Veerle , Schalm Olivier , Houbraken Jos , Thomas Mienke , Meesdom Eva , Devos Annemie , Dooren Rita Van , Nieuwdorp Hans , Janssen Elsje , Janssens Koen
Published: August 2009

In this study, the results of analysing of a series of 16th–19th century painted enamel objects of the Limoges School currently in collections in three Dutch and Flemish museums by means of portable and micro x‐ray fluorescence analysis (PXRF and µ‐XRF) and electron probe micro analysis (EPMA) are presented. The aim of the investigation was the authentication of specific pieces. Therefore, the glass compositions as well as the (glass) colouring agents used by the Limoges' artists were studied as a function of the age of the objects. Due to the evolution of these properties, it is possible to approximately date these objects based on their chemical composition. The complete ‘émail peint’ collection of the Museum Boijmans‐Van Beuningen (Rotterdam, The Netherlands), consisting of 20 ‘émail peint’ plaques, was analysed with µ‐XRF. Quantitative information was obtained by EPMA analysis of 15 enamel fragments of objects from museum and private collections in the Low Countries. PXRF analyses were performed on the painted enamel collection of the Antwerp Vleeshuis Museum (13 objects) and the Mayer van den Bergh Museum (4 objects) and on a set of 18 plaques that were donated to the Boijmans‐Van Beuningen Museum by a private collector.

The results obtained by means of EPMA, µ‐XRF and PXRF proved to be useful in the discrimination of 16th century painted enamel objects from those of the19th century. From a total of 70 objects examined, 2 objects (OM964A and OM993) featured a chemical signature that deviated from the published literature composition and pigment use consistent with its presumed period of manufacture. Copyright © 2009 John Wiley & Sons, Ltd.
Characterization of Silica Gels by 29Si MAS NMR and IR Spectroscopic Measurements
Authors: Lutz Wolfgang , Täschner Dirk , Kurzhals Rolf , Heidemann Detlef , Hübert Cornelia
Published: August 2009

The solubility of commercial and synthesized silica gels in a solution of Tetra‐Ethyl‐Ammonium‐Hydroxide (TEAOH) was investigated at room temperature. The state of parent silica frameworks was characterized by BET and SEM. The structural defects were identified both by the Qn group analysis in 29Si MAS NMR and IR spectroscopic investigation. It was found that the dissolution rate of the samples shows a tendency for growing up with an increasing BET surface. The increase of the internal surface was accompanied by formation of Si(OSi)3(OH) (Q3) and Si(OSi)2(OH)2 (Q2) structural units. The higher the number of Q3 and Q2 groups observed, the faster the samples were dissolved in TEAOH solution due to the attack of the hydroxide ions on the terminal OH groups of the framework. The asymmetrical TOT valence vibration of the IR spectra was systematically shifted to lower values with increase in the number of Q3 and Q2 structure groups.
Cancer and Obesity: Effect of Bariatric Surgery
Authors: Adams Ted D. , Hunt Steven C.
Published: August 2009

Recent international cancer prevention guidelines recommend weight loss, where appropriate, for the purpose of cancer risk reduction. However, limited research associates voluntary weight loss to subsequent cancer incidence because of the difficulty of achieving long‐term weight loss maintenance among large participant groups. Bariatric surgery has demonstrated long‐term sustained weight loss, and as a result, patients after bariatric surgery represent an ideal population to explore the relationship between long‐term, voluntary weight loss and cancer incidence. This paper briefly reviews cancers that have shown to be associated with overweight and obesity and looks at studies that demonstrate reduced total mortality after bariatric surgery. Reduced cancer mortality and incidence as well as reduced cancer‐related physician visits after bariatric surgery are presented. Study limitations and future research questions related to cancer and bariatric surgery are briefly discussed.
Surgeons Without Borders: A Brief History of Surgery at Médecins Sans Frontières
Authors: Chu Kathryn , Rosseel Peter , Trelles Miguel , Gielis Pierre
Published: August 2009

Médecins Sans Frontières (MSF) is a humanitarian organization that performs emergency and elective surgical services in both conflict and non‐conflict settings in over 70 countries. In 2006 MSF surgeons departed on approximately 125 missions, and over 64,000 surgical interventions were carried out in some 20 countries worldwide. Historically, the majority of MSF surgical projects began in response to conflicts or natural disasters. During an emergency response, MSF has resources to set up major operating facilities within 48 h in remote areas. One of MSF strengths is its supply chain. Large pre‐packaged surgical kits, veritable “operating theatres to go,” can be readied in enormous crates and quickly loaded onto planes. In more stable contexts, MSF has also strengthened the delivery of surgical services within a country’s public health system. The MSF surgeon is the generalist in the broadest sense and performs vascular, obstetrical, orthopaedic, and other specialized surgical procedures. The organization aims to provide surgical services only temporarily. When there is a decrease in acute needs a program will be closed, or more importantly, turned over to the Ministry of Health or another non‐governmental organization. The long‐term solution to alleviating the global burden of surgical disease lies in building up a domestic surgical workforce capable of responding to the major causes of surgery‐related morbidity and mortality. However, given that even countries with the resources of the United States suffer from an insufficiency of surgeons, the need for international emergency organizations to provide surgical assistance during acute emergencies will remain for the foreseeable future.
Competitive RT-PCR Strategy for Quantitative Evaluation of the Expression of Tilapia (Oreochromis niloticus) Growth Hormone Receptor Type I
Authors: Rodríguez-Mallon Alina , Cárdenas Yamilet , Lugo Juana María , Oliva Aymé , Morales Antonio , Estrada Mario Pablo
Published: August 2009

Quantization of gene expression requires that an accurate measurement of a specific transcript is made. In this paper, a quantitative reverse transcription-polymerase chain reaction (RT-PCR) by competition for tilapia growth hormone receptor type I is designed and validated. This experimental procedure was used to determine the abundance of growth hormone receptor type I transcript in different tilapia tissues. The results obtained with this developed competitive RT-PCR were similar to real-time PCR results reported recently. This protocol provides a reliable alternative, but less expensive than real-time PCR to quantify specific genes.
Computational Biology Methods and Their Application to the Comparative Genomics of Endocellular Symbiotic Bacteria of Insects
Authors: Commins Jennifer , Toft Christina , Fares Mario A
Published: August 2009

Comparative genomics has become a real tantalizing challenge in the postgenomic era. This fact has been mostly magnified by the plethora of new genomes becoming available in a daily bases. The overwhelming list of new genomes to compare has pushed the field of bioinformatics and computational biology forward toward the design and development of methods capable of identifying patterns in a sea of swamping data noise. Despite many advances made in such endeavor, the ever-lasting annoying exceptions to the general patterns remain to pose difficulties in generalizing methods for comparative genomics. In this review, we discuss the different tools devised to undertake the challenge of comparative genomics and some of the exceptions that compromise the generality of such methods. We focus on endosymbiotic bacteria of insects because of their genomic dynamics peculiarities when compared to free-living organisms.
In Vivo Imaging of Far-red Fluorescent Proteins after DNA Electrotransfer to Muscle Tissue
Authors: Hojman Pernille , Eriksen Jens , Gehl Julie
Published: August 2009

DNA electrotransfer to muscle tissue yields long-term, high levels of gene expression; showing great promise for future gene therapy. We want to characterize the novel far-red fluorescent protein Katushka as a marker for gene expression using time domain fluorescence in vivo imaging. Highly efficient transgenic expression was observed after DNA electrotransfer with 100-fold increase in fluorescent intensity. The fluorescent signal peaked 1 week after transfection and returned to background level within 4 weeks. Katushka expression was not as stable as GFP expression, which was detectable for 8 weeks. Depth and 3D analysis proved that the expression was located in the target muscle. In vivo bio-imaging using the novel Katushka fluorescent protein enables excellent evaluation of the transfection efficacy, and spatial distribution, but lacks long-term stability.
Detection and Processing Techniques of FECG Signal for Fetal Monitoring
Authors: Hasan MA , Reaz MBI , Ibrahimy MI , Hussain MS , Uddin J
Published: August 2009

Fetal electrocardiogram (FECG) signal contains potentially precise information that could assist clinicians in making more appropriate and timely decisions during labor. The ultimate reason for the interest in FECG signal analysis is in clinical diagnosis and biomedical applications. The extraction and detection of the FECG signal from composite abdominal signals with powerful and advance methodologies are becoming very important requirements in fetal monitoring. The purpose of this review paper is to illustrate the various methodologies and developed algorithms on FECG signal detection and analysis to provide efficient and effective ways of understanding the FECG signal and its nature for fetal monitoring. A comparative study has been carried out to show the performance and accuracy of various methods of FECG signal analysis for fetal monitoring. Finally, this paper further focused some of the hardware implementations using electrical signals for monitoring the fetal heart rate. This paper opens up a passage for researchers, physicians, and end users to advocate an excellent understanding of FECG signal and its analysis procedures for fetal heart rate monitoring system.
A Method for Structure–Activity Analysis of Quorum-Sensing Signaling Peptides from Naturally Transformable Streptococci
Authors: Tian XiaoLin , Syvitski Raymond T , Liu TianLei , Livingstone Nadine , Jakeman David L , Li Yung-Hua
Published: August 2009

Many species of streptococci secrete and use a competence-stimulating peptide (CSP) to initiate quorum sensing for induction of genetic competence, bacteriocin production, and other activities. These signaling molecules are small, unmodified peptides that induce powerful strain-specific activity at nano-molar concentrations. This feature has provided an excellent opportunity to explore their structure–function relationships. However, CSP variants have also been identified in many species, and each specifically activates its cognate receptor. How such minor changes dramatically affect the specificity of these peptides remains unclear. Structure–activity analysis of these peptides may provide clues for understanding the specificity of signaling peptide–receptor interactions. Here, we use the Streptococcus mutans CSP as an example to describe methods of analyzing its structure–activity relationship. The methods described here may provide a platform for studying quorum-sensing signaling peptides of other naturally transformable streptococci.
A Framework for White Blood Cell Segmentation in Microscopic Blood Images Using Digital Image Processing
Authors: Sadeghian Farnoosh , Seman Zainina , Ramli Abdul Rahman , Abdul Kahar Badrul Hisham , Saripan M-Iqbal
Published: August 2009

Evaluation of blood smear is a commonly clinical test these days. Most of the time, the hematologists are interested on white blood cells (WBCs) only. Digital image processing techniques can help them in their analysis and diagnosis. For example, disease like acute leukemia is detected based on the amount and condition of the WBC. The main objective of this paper is to segment the WBC to its two dominant elements: nucleus and cytoplasm. The segmentation is conducted using a proposed segmentation framework that consists of an integration of several digital image processing algorithms. Twenty microscopic blood images were tested, and the proposed framework managed to obtain 92% accuracy for nucleus segmentation and 78% for cytoplasm segmentation. The results indicate that the proposed framework is able to extract the nucleus and cytoplasm region in a WBC image sample.
Lentiviral-Mediated Transgene Expression Can Potentiate Intestinal Mesenchymal-Epithelial Signaling
Authors: Dismuke Adria D , Kohn Aimee D , Moon Randall T , Wong Melissa H
Published: August 2009

Mesenchymal-epithelial signaling is essential for the development of many organs and is often disrupted in disease. In this study, we demonstrate the use of lentiviral-mediated transgene delivery as an effective approach for ectopic transgene expression and an alternative to generation of transgenic animals. One benefit to this approach is that it can be used independently or in conjunction with established transgenic or knockout animals for studying modulation of mesenchymal-epithelial interactions. To display the power of this approach, we explored ectopic expression of a Wnt ligand in the mouse intestinal mesenchyme and demonstrate its functional influence on the adjacent epithelium. Our findings highlight the efficient use of lentiviral-mediated transgene expression for modulating mesenchymal-epithelial interactions in vivo.
Laparoscopic vaginal reconstruction using an ileal segment
Authors: Wu Ji‐Xiang , Li Bin , Li Wen‐Zhi , Jiang Yong‐Guang , Liang Jie‐Xiong , Zhong Chen‐Xi
Published: August 2009

Objective

To evaluate the feasibility of laparoscopic vaginal reconstruction using an ileal segment in patients with vaginal atresia, male‐female transsexual patients, or patients who had vaginal cancer.

Methods

A retrospective review of the records of 80 patients who underwent laparoscopic vaginoplasty between 2004 and 2007 at Beijing Anzhen Hospital, China.

Results

Nineteen (23.8%) patients underwent total laparoscopic vaginoplasty and 61 (76.3%) underwent laparoscope‐assisted vaginoplasty. There were 64 (80.0%) primary operations and 16 (20.0%) secondary operations. All of the surgeries were completed successfully and no intraoperative complications occurred. Mean follow‐up time was 14 months. Postoperatively, 5 women had vaginal stenosis, while 4 women had no sexual partner during the follow‐up period which meant that they could not be assessed completely. The remaining 71 patients were satisfied with their sexual lives after surgery.

Conclusion

Vaginal reconstruction performed via total laparoscopic vaginoplasty or a laparoscope‐assisted technique using an ileal segment has a high success rate for a functional vagina and patient satisfaction.
Role of methicillin-resistant Staphylococcus aureus in head and neck infections
Authors: Brook I
Published: August 2009

The prevalence of infection with methicillin-resistant Staphylococcus aureus is increasing. Methicillin-resistant Staphylococcus aureus is also being recognised as an important pathogen in head and neck infections. This review summarises studies published over the past two decades which illustrate the growing prevalence of methicillin-resistant Staphylococcus aureus, and the current therapeutic approaches to head and neck infections caused by this bacterium. These infections include sinusitis, otitis, periorbital cellulitis, cervical lymphadenitis, tonsillitis, thyroiditis, retropharyngeal abscess, and abscesses and wounds of the neck. Treatment of head and neck infections associated with methicillin-resistant Staphylococcus aureus includes drainage and debridement, as well as administration of local and systemic antimicrobials that provide coverage against these organisms and against potential aerobic and anaerobic pathogens that may be present if the infection is polymicrobial.
Robust backstepping control of an underactuated one-legged hopping robot in stance phase
Authors: He Guangping , Geng Zhiyong
Published: August 2009

Exponentially stabilizing a non-Spring Loaded Inverted Pendulum (SLIP) model-based one-legged hopping robot in stance phase is studied. Differing from the SLIP model systems, the hopping robot with non-SLIP model considered in this paper does not restrict the center of mass of the robot coinciding to the hip joint. A specific underactuated one-legged hopping robot with two actuated arms are selected to investigate the dynamics and control problem. It is shown that the system holds the essential nonlinear prosperities of general systems and belongs to a class of second-order nonholonomic mechanical systems, which cannot be stabilized by any smooth time-invariant state feedback. By using a coordinates transform based on the so-called normalized momentum, a robust backstepping control method is presented for the specific hopping robot system. Both theoretical analysis and numerical simulations show that the robust backstepping controller can stabilize the underactuated one-legged hopping robot to its balance configuration as well as a periodic motion trajectory near to the balance configuration. These results are significative for designing a new non-SLIP model based hopping robot systems with more biological characteristics.
Investigation of axial forces on dynamic properties of a flexible 3-PRR planar parallel manipulator moving with high speed
Authors: Zhang Xuping , Mills James K. , Cleghorn William L.
Published: August 2009

The effect of axial forces on the dynamic properties is formulated and investigated for a 3-PRR planar parallel manipulator with three flexible intermediate links. A dynamic model of the manipulator system is developed based on the assumed mode method with the consideration of the effect of longitudinal forces on lateral stiffness is included. The flexible intermediate links are modeled as Euler–Bernoulli beams with pinned-pinned boundary conditions, which are verified by experimental modal tests. Natural frequencies of bending vibration of the intermediate links are derived as the functions of axial force and rigid-body motion of the manipulator. Dynamic behavior including the effect of axial forces on lateral deformation is investigated, and configuration-dependant frequencies are analyzed. Numerical simulations of configuration-dependent frequency properties and axial forces are performed to illustrate the effect of axial forces on the dynamic behaviors of the flexible parallel manipulator. Simulation results of mode amplitudes, deformations, axial forces, inertial, and coupling forces are presented, and further validate the theoretical derivations. These analyses and results provide a new and valuable insight to the design and control of the parallel manipulators with flexible intermediate links.
Identifying and Locating–Dominating Codes in (Random) Geometric Networks
Authors: MÜLLER T. , SERENI J.-S.
Published: August 2009

We model a problem about networks built from wireless devices using identifying and locating–dominating codes in unit disk graphs. It is known that minimizing the size of an identifying code is -complete even for bipartite graphs. First, we improve this result by showing that the problem remains -complete for bipartite planar unit disk graphs. Then, we address the question of the existence of an identifying code for random unit disk graphs. We derive the probability that there exists an identifying code as a function of the radius of the disks, and we find that for all interesting ranges of r this probability is bounded away from one. The results obtained are in sharp contrast to those concerning random graphs in the Erdős–Rényi model. Another well-studied class of codes is that of locating–dominating codes, which are less demanding than identifying codes. A locating–dominating code always exists, but minimizing its size is still -complete in general. We extend this result to our setting by showing that this question remains -complete for arbitrary planar unit disk graphs. Finally, we study the minimum size of such a code in random unit disk graphs, and we prove that with probability tending to one, it is of size (n/r)2/3+o(1) if r ≤ /2−ϵ is chosen such that nr2 → ∞, and of size n1+o(1) if nr2 ≪ lnn.
Lighting the blue touch paper, and building well
Authors: Platt Christopher , Spier Steven
Published: August 2009

Architectural practice has become considerably more complex in the last twenty years, not to mention since the days of Wright. Many more professions are involved in realising a building, and the construction industry has become professionalised in areas such as health and safety, management training and continuing professional development. Procurement methods for buildings are proliferating and roles for all involved changing, especially for the architect. Shorter timescales are common and there is a general consensus that, in the UK at least, there is a serious skills shortage in the industry and a decline in the quality of the building trades. The industry has become both more litigious and more international.
Double staircases and the vertical distribution of housing in Venice 1450–1600
Authors: Good Robert
Published: August 2009

This paper presents changes in the vertical circulation and organisation of merchant palaces, and their influence on multi-family architecture in Venice from 1450 to 1600. Just prior to this period buildings underwent a substantial change in the vertical distribution of floors; this marked the transfer of the commercial-residence casa fondaco prototype into a more complex multi-level building with two semi-autonomous piani nobili palatial apartments. The resulting vertical expansion led to a departure away from the external courtyard staircase as the primary means of vertical circulation. Many Late Gothic palatial buildings incorporated double courtyard staircases that provided individual access to each palatial apartment. However, this scheme consumed a great deal of developable land resulting in the widespread utilisation of interior monumental dog-leg staircases by the Early Renaissance. This simplified internal staircase fitted cleanly into the existing structural logic of both new and remodelled palace buildings.
Harmonic and equianharmonic equations in the Grothendieck–Teichmüller group. III
Authors: Nakamura Hiroaki , Tsunogai Hiroshi , Yasuda Seidai
Published: August 2009

We study behaviours of the ‘equianharmonic’ parameter of the Grothendieck–Teichmüller group introduced by Lochak and Schneps. Using geometric construction of a certain one-parameter family of quartics, we realize the Galois action on the fundamental group of a punctured Mordell elliptic curve in the standard Galois action on a specific subgroup of the braid group $\smash{\hat{B}_4}$. A consequence is to represent a matrix specialization of the ‘equianharmonic’ parameter in terms of special values of the adelic beta function introduced and studied by Anderson and Ihara.
On the equations for universal torsors over del Pezzo surfaces
Authors: Serganova Vera V. , Skorobogatov Alexei. N.
Published: August 2009

We describe equations of the universal torsors over del Pezzo surfaces of degrees from 2 to 5 over an algebraically closed field in terms of the equations of the corresponding homogeneous space G/P. We also give a generalization for fields that are not algebraically closed.
Supersingular Kottwitz–Rapoport strata and Deligne–Lusztig varieties
Authors: Görtz Ulrich , Yu Chia-Fu
Published: August 2009

We investigate the special fibres of Siegel modular varieties with Iwahori level structure. On these spaces, we have the Newton stratification, and the Kottwitz–Rapoport (KR) stratification; one would like to understand how these stratifications are related to each other. We give a simple description of all KR strata which are entirely contained in the supersingular locus as disjoint unions of Deligne–Lusztig varieties. We also give an explicit numerical description of the KR stratification in terms of abelian varieties.
Foreshock compressional boundary
Authors: Omidi N. , Sibeck D. G. , Blanco‐Cano X.
Published: August 2009

We employ 2.5‐D electromagnetic, hybrid simulations that treat ions kinetically via particle‐in‐cell methods and electrons as a massless fluid to study the formation and properties of a newly discovered boundary named the foreshock compressional boundary (FCB). This boundary forms in the ion foreshock and is associated with enhanced densities and magnetic field strengths. At times, but not always, the FCB separates the pristine solar wind plasma from the ion foreshock. In this study, we investigate the dependence of FCB characteristics on solar wind Mach number and cone angle (the angle between flow velocity and interplanetary magnetic field). We show that the strength of the foreshock compressional boundary increases with the Mach number. This enhancement is in turn tied to the density and velocity of the backstreaming ions in the foreshock whose interaction with the solar wind results in ULF turbulence which is ultimately responsible for the formation of FCB. During small cone angles the foreshock compressional boundary is symmetric with respect to the radial direction. As the cone angle increases, the FCB becomes less symmetric and eventually is confined to one side of the foreshock. The strength of the FCB also decreases with increasing cone angle but depending on the Mach number can exist for cone angles of 40° and beyond. A recent study that compared data from a global hybrid simulation of the foreshock with Cluster spacecraft observations showed that encounters with foreshock cavities can be interpreted as back and forth motion of a FCB causing spacecraft to move from the solar wind through the FCB into the foreshock and back into solar wind. An example of a FCB observed by the Cluster spacecraft is presented and shown to be in general agreement with model predictions.
An optimized estimate of glacial melt from the Ross Ice Shelf using noble gases, stable isotopes, and CFC transient tracers
Authors: Loose B. , Schlosser P. , Smethie W. M. , Jacobs S.
Published: August 2009

Isotopes of helium and neon and the H218O/H216O ratio of water are proven proxies for melt from glacial ice beneath floating ice shelves and at ice shelf fronts. Their high concentrations in glacial meltwater, compared to other environmental sources, make them ideal tracers for studies of the pathways of glacial meltwater from its origins into the ocean interior. We combine noble gas and stable isotopes with temperature, salinity, and dissolved oxygen measurements from three cruises (along the Ross Ice Shelf during the austral summers of 1993–1994 and 1999–2000 and to the Ross Sea in 2000–2001) and use optimal multiparameter analysis to compute the water mass concentration, including glacial meltwater. The distribution of meltwater at the front of the Ross Ice Shelf extended east from 180°W, with the highest concentrations found near 165°W in both 1994 and 2000. The mean meltwater concentration at the ice shelf front was 2.0 ± 0.33‰ in 1994, 2.2 ± 0.36‰ in 2000, and 0.25 ± 0.1‰ in the western Ross Sea in 2001. Water mass concentrations are used to correct for bias in the CFC age, introduced by mixing with CFC‐free waters, an effect revealed by comparing CFC age with transit time distribution curves. The water residence time within the ice shelf cavity, using CFCs and the mean meltwater concentration, implies a basal melt rate of 33–50 km3 a−1.
Statistical characterization of Geosat altimetry noise: Dependence on environmental parameters
Authors: Goff John A.
Published: August 2009

Sea surface height (SSH) measurements from the Geosat satellite altimetry mission are analyzed to statistically characterize their noise process, which is defined here as the small‐scale (<50 km), time‐varying component of the altimetry data. This analysis is one component of a larger effort to extract meaningful information about seafloor roughness from the small‐scale fabric of the altimetric gravity field. Both small‐scale seafloor topography (e.g., abyssal hills) and SSH noise significantly influence the measured gravity fabric. Hence, a global, quantitative understanding of SSH noise is required to infer what portion of the gravity fabric is associated with the true geoid. It is also anticipated that the SSH noise analysis will prove useful in designing improvements to altimetry processing algorithms. The SSH data are first processed by differencing nearest‐neighbor tracks, to minimize the static component of variability, and then by high‐pass filtering, to remove variability associated with mesoscale oceanic circulation. Autocovariance analysis reveals that SSH noise can be decomposed into uncorrelated (white noise) and correlated, semiperiodic components. Three parameters are measured which characterize the variance of both components and the correlation length of the correlated component. The global distribution of uncorrelated noise variance is closely correlated to significant wave heights, directly linking the uncertainty of the altimeter return time to the roughness of the sea surface. The variance and correlation length of the correlated component of noise can be associated with three separate environmental parameters: sea ice, precipitation rates, and upper atmospheric variability associated with the subtropical jet stream. As widely differing as these environmental processes are, it is hypothesized that features like sea ice, rain storms, and atmospheric turbulence can cause sudden perturbations in the return time of the altimetry signal, creating decaying oscillations associated with the onboard tracking algorithms.
Correlation properties of magnetosheath magnetic field fluctuations
Authors: Gutynska O. , Šafránková J. , Němeček Z.
Published: August 2009

The magnetosheath is characterized by a variety of low‐frequency fluctuations, but their features and sources are different. Taking advantage of multipoint magnetic field measurements of the Cluster spacecraft, we present a statistical study to reveal properties of waves. We compute cross‐correlation coefficients of magnetic field strengths as measured by pairs of the Cluster spacecraft and determine the correlation length of magnetosheath waves. We discuss the relationship between the correlation length and upstream parameters as well as its connection with the wave mode and frequency power spectrum. In the frequency interval of 0.001–0.125 Hz, we found that the correlation length of fluctuations increases (1) through intervals of high solar wind speeds, (2) with increasing interplanetary magnetic field (IMF) strength, (3) if the cross‐correlation between the IMF and magnetosheath magnetic field is higher, and (4) if the amplitude of fluctuations is larger.
Adverse Effects of Trichothiodystrophy DNA Repair and Transcription Gene Abnormalities on Human Fetal Development
Authors: Moslehi Roxana , Signore Caroline , Troendle James , Dzutsev Amiran , Mills James
Published: August 2009

The effects of DNA repair and transcription genes in human prenatal life have never been studied. Trichothiodystrophy (TTD) is a rare (affected frequency of 10^-6^) recessive disorder caused by mutations in genes involved in the nucleotide excision repair (NER) pathway and in transcription. Based on our clinical observations, we conducted a genetic epidemiologic study to investigate gestational outcomes associated with TTD. We compared pregnancies resulting in TTD-affected offspring (N=24) with respect to abnormalities in their antenatal and neonatal periods to pregnancies resulting in their unaffected siblings (N=18), accounting for correlation, and to population reference values. Significantly higher incidence of several severe gestational complications was noted in TTD-affected pregnancies. Gestational complications were noted in nearly all pregnancies resulting in TTD-affected offspring with XPD and TTDN1, but not TTD-A, gene mutations. Abnormal placental development may explain the constellation of observed complications; therefore, we hypothesize that some TTD genes play an important role in normal placental and fetal development. We investigated this hypothesis by analyzing the expression patterns of TTD genes. Expression of TTDA was strongly negatively correlated (r=-0.7,P<0.0001) with gestational age, while XPD, XPB and TTDN1 were consistently expressed from 14 to 40 weeks gestation. *Conclusion:* Our results indicate an important role for XPD, XPB and TTDN1 gene products during normal human placental and fetal development.
Laguerre-type derivatives: Dobiński relations and combinatorial identities
Authors: Penson K. A. , Blasiak P. , Horzela A. , Duchamp G. H. E. , Solomon A. I.
Published: August 2009

We consider properties of the operators D(r,M)=ar(a†a)M (which we call generalized Laguerre-type derivatives), with r=1,2,…, M=0,1,…, where a and a† are boson annihilation and creation operators, respectively, satisfying [a,a†]=1. We obtain explicit formulas for the normally ordered form of arbitrary Taylor-expandable functions of D(r,M) with the help of an operator relation that generalizes the Dobiński formula. Coherent state expectation values of certain operator functions of D(r,M) turn out to be generating functions of combinatorial numbers. In many cases the corresponding combinatorial structures can be explicitly identified.
Coherent acoustic vibrations in silicon submicron spiral arrays
Authors: Yamaguchi Masashi , Liu Jianxun , Ye Dexian , Lu Toh-Ming
Published: August 2009

Mechanical properties of complex silicon submicron structures have been studied both experimentally and theoretically using time resolved ultrafast spectroscopy and finite element analysis. Periodic and random arrays of single-turned silicon submircron spirals were grown using the oblique angle deposition technique. Resonant vibrational modes of the submicron spirals were coherently excited by femtosecond laser pulses. Excitation of multiple harmonics of the resonant vibrations has been observed, and the mode patterns of the excited vibrations in the submicron spirals have been calculated.
Layer growth and connectivity calculations based on a stick-ball model: Application to silicon nanocrystals
Authors: Voigt Felix , Bauer Gottfried H. , Huisken Friedrich
Published: August 2009

Monte Carlo computer simulations based on a stick-ball model were performed in order to simulate the growth of layers built from nanoparticles impinging on a substrate. From the simulations, a bulk layer porosity P∞=0.85±0.01 was extracted. Furthermore, characteristics about the percolative charge transport during layer growth were deduced. The establishment of the first contact between coplanar contacts via paths through nanoparticles was investigated for a variety of geometrical parameters. The onset of conductance in the simulations after the establishment of the first contact can be well described by a shifted power law. The simulations were compared with experimental results on layers built from Si nanocrystals and good qualitative and to some extent quantitative agreement was found. A tolerance parameter was introduced into the simulations referring to the maximum distance at which tunneling between adjacent nanoparticles may occur. By choosing different tolerance values and extrapolating the data to comply with the experimental results, a tolerance parameter of 0.73 nm was estimated.
Efficient and accurate approximations to the local coupled cluster singles doubles method using a truncated pair natural orbital basis
Authors: Neese Frank , Hansen Andreas , Liakos Dimitrios G.
Published: August 2009

A production level implementation of the closed-shell local quadratic configuration interaction and coupled cluster methods with single and double excitations (QCISD and CCSD) based on the concept of pair natural orbitals [local pair natural orbital LPNO-QCISD and LPNO-CCSD) is reported, evaluated, and discussed. This work is an extension of the earlier developed LPNO coupled-electron pair approximation (LNPO-CEPA) method [F. Neese et al., Chem. Phys. 130, 114108 (2009)] and makes extended use of the resolution of the identity (RI) or density fitting (DF) approximation. Two variants of each method are compared. The less accurate approximations (LPNO2-QCISD/LPNO2-CCSD) still recover 98.7%–99.3% of the correlation energy in the given basis and have modest disk space requirements. The more accurate variants (LPNO1-QCISD/LPNO1-CCSD) typically recover 99.75%–99.95% of the correlation energy in the given basis but require the Coulomb and exchange operators with up to two-external indices to be stored on disk. Both variants have comparable computational efficiency. The convergence of the results with respect to the natural orbital truncation parameter (TCutPNO) has been studied. Extended numerical tests have been performed on absolute and relative correlation energies as function of basis set size and TCutPNO as well as on reaction energies, isomerization energies, and weak intermolecular interactions. The results indicate that the errors of the LPNO methods compared to the canonical QCISD and CCSD methods are below 1 kcal/mol with our default thresholds. Finally, some calculations on larger molecules are reported (ranging from 40–86 atoms) and it is shown that for medium sized molecules the total wall clock time required to complete the LPNO-CCSD calculations is only two to four times that of the preceding self-consistent field (SCF). Thus these methods are highly suitable for large-scale computational chemistry applications. Since there are only three thresholds involved that have been given conservative default values, the methods can be confidentially used in a “black-box” fashion in the same way as their canonical counterparts.
Nonreciprocity in circular magnetoplasma-filled waveguides above the cyclotron frequency
Authors: Alshannaq Shadi S. , Rojas Roberto G.
Published: August 2009

The electromagnetic behavior of a circular perfect electric conductor waveguide with various magnetoplasma filling configurations has been investigated near the cyclotron resonance region at 77 K with longitudinal magnetic bias. Faraday rotation in the forward and reverse directions along with the waveguide geometry effect provided the nonreciprocal attenuation to design an isolator for frequencies up to the terahertz region. Based on the finite element method, two-dimensional eigenvalue as well as three-dimensional numerical simulations are provided to illustrate the phenomena. Unprecedented performance was attained for the coaxial configuration in terms of the bias-to-frequency ratio. Other configurations were found to have some nonreciprocity as well.
Nonlinear dynamics in GaAs1−xNx diodes under terahertz radiation
Authors: Feng W. , Cao J. C.
Published: August 2009

We carry out a theoretical study of nonlinear dynamics in terahertz-driven n+nn+ GaAs1−xNx diodes. A cooperative nonlinear oscillatory mode shows up due to the negative differential velocity (NDV) effect in the highly nonparabolic conduction band of the diodes. We have made detailed investigations to the complicated chaotic dynamics by changing the dc bias, ac amplitude, and ac frequency of terahertz fields with chaos-detecting methods, such as Poincaré bifurcation diagram, power spectrum, and first return map. The influence of NDV curves on the nonlinear dynamics is also studied. The coupling of dc bias and ac driving voltage causes possible types of transport states (periodic or chaotic) and transitions between them. The resulting power spectrum pattern displays a very complex mosaic scenario with a self-similar emergence of high-order mixing frequencies.
The Stark effect in Rydberg states of a highly polar diatomic molecule: CaF
Authors: Petrović Vladimir S. , Kay Jeffrey J. , Coy Stephen L. , Field Robert W.
Published: August 2009

The Stark effect in molecular Rydberg states is qualitatively different from the Stark effect in atomic Rydberg states because of the anisotropy of the ion core and the existence of rotational and vibrational degrees of freedom. These uniquely molecular features cause the electric-field-induced decoupling of the Rydberg electron from the body frame to proceed in several stages in a molecule. Because the transition dipole moment among the same-n* Rydberg states is much larger than the permanent dipole moment of the ion core, the decoupling of the Rydberg electron from the ion core proceeds gradually. In the first stage, analyzed in detail in this paper, l and N are mixed by the external electric field, while N+ is conserved. In the further stages, as the external electric field increases, N+, n*, and v+ are expected to undergo mixing. We have characterized these stages in n*=13, v+=1 states of CaF. The large permanent dipole moment of CaF+ makes CaF qualitatively different from the other molecules in which the Stark effect in Rydberg states has been described (H2, Na2, Li2, NO, and H3) and makes it an ideal testbed for documenting the competition between the external and CaF+ dipole electric fields. We use the weak-field Stark effect to gain access to the lowest-N rotational levels of f, g, and h states and to assign their actual or nominal N+ quantum number. Lowest-N rotational levels provide information needed to disentangle the short-range and long-range interactions between the Rydberg electron and the ion core. We diagonalize an effective Hamiltonian matrix to determine the l-characters of the 3⩽l⩽5 core-nonpenetrating Σ+2 states and to characterize their mixing with the core-penetrating states. We conclude that the mixing of the l=4, N−N+=−4(g(−4)) state with lower-l Σ+2 states is stronger than documented in our previous multichannel quantum defect theory and long-range fits to zero-field spectra.
Large-area monocrystalline silicon thin films by annealing of macroporous arrays: Understanding and tackling defects in the material
Authors: Depauw Valérie , Gordon Ivan , Beaucarne Guy , Poortmans Jef , Mertens Robert , Celis Jean-Pierre
Published: August 2009

A concept that could provide a thin monocrystalline-silicon absorber layer without resorting to the expensive step of epitaxy would be very appealing for reducing the cost of solar cells. The empty-space-in-silicon technique by which thin films of silicon can be formed by reorganization of regular arrays of cylindrical voids at high temperature may be such a concept if the high quality of the thin film could be ensured on centimeter-large areas. While previous works mainly investigated the influence of the porous array on the final structure, this work focuses on the practical aspects of the high-temperature step and its application to large areas. An insight into the defects that may form is given and the origin of these defects is discussed, providing recommendations on how to avoid them. Surface roughening, pitting, formation of holes, and silicon pillars could be attributed to the nonuniform reactions between Si, SiO2, and SiO. Hydrogen atmospheres are therefore preferred for reorganization of macroporous arrays. Argon atmospheres, however, may provide high-quality silicon thin films as well, possibly even more easily transferable, as long as annealing is performed in controlled, clean, and oxygen-free conditions. Our experiments on large areas also highlight the importance of kinetics, which had not been considered up to now and which will require further understanding to ensure a complete reorganization over any wafer area.
Parallel generation of nanochannels in fused silica with a single femtosecond laser pulse: Exploiting the optical near fields of triangular nanoparticles
Authors: Hubenthal F. , Morarescu R. , Englert L. , Haag L. , Baumert T. , Träger F.
Published: August 2009

We present experiments to prepare highly ordered nanochannels with subdiffraction dimensions on fused silica surfaces with femtosecond laser light. For this purpose, we exploit the strongly enhanced near field of highly ordered triangular gold nanoparticles. We demonstrate that after a single laser shot, 6 μm long nanochannels with a mean depth of 4 nm and an average width of 96 nm, i.e., well below the diffraction limit, are generated. These nanochannels are prepared by ablation, caused by the localization of the near field. The crucial parameters, besides the applied fluence, are the polarization direction of the incoming laser light with respect to the triangular nanoparticles and the size of the nanoparticles.
A group theoretical identification of integrable cases of the Liénard-type equation ẍ+f(x)ẋ+g(x)=. I. Equations having nonmaximal number of Lie point symmetries
Authors: Pandey S. N. , Bindu P. S. , Senthilvelan M. , Lakshmanan M.
Published: August 2009

We carry out a detailed Lie point symmetry group classification of the Liénard-type equation, ẍ+f(x)ẋ+g(x)=0, where f(x) and g(x) are arbitrary smooth functions of x. We divide our analysis into two parts. In the present first part we isolate equations that admit lesser parameter Lie point symmetries, namely, one, two, and three parameter symmetries, and in the second part we identify equations that admit maximal (eight) parameter Lie point symmetries. In the former case the invariant equations form a family of integrable equations, and in the latter case they form a class of linearizable equations (under point transformations). Further, we prove the integrability of all the equations obtained in the present paper through equivalence transformations either by providing the general solution or by constructing time independent Hamiltonians. Several of these equations are being identified for the first time from the group theoretical analysis.
Interaction between silver nanowires and CO on a stepped platinum surface
Authors: Streber R. , Tränkenschuh B. , Schöck J. , Papp C. , Steinrück H.-P. , McEwen J.-S. , Gaspard P. , Denecke R.
Published: August 2009

We studied the interplay between Ag decoration of a stepped Pt(355) surface and CO adsorption by in situ high-resolution x-ray photoelectron spectroscopy. Varying amounts of Ag deposited at 300 K initially lead to a row-by-row growth starting from the lower Pt step edges. Such decoration of the step sites results in a change in the CO adsorption behavior. An apparent blocking of step sites for low CO coverages is attributed to a change in the electronic structure, resulting in a C 1s binding energy of CO at step sites being equal to that for CO at terrace on-top sites in the presence of Ag. Higher CO coverages induce the formation of embedded Ag clusters within the upper terraces, thus freeing up a part of the original Pt step sites for CO adsorption, as was derived by a comparison to density functional theory calculations in the corresponding surface models.
Crystal structure, electric field gradient, and electronic charge densities in ReB2: A single crystal x-ray, B11 nuclear magnetic resonance, and first-principles study
Authors: Żogał O. J. , Fojud Z. , Herzig P. , Pietraszko A. , Lyashchenko A. B. , Jurga S. , Paderno V. N.
Published: August 2009

We have grown a single crystal of ReB2 and refined its crystal structure. Our structural studies confirmed the hexagonal structure (space group P63/mmc) with lattice parameters a=2.8982(1) Å and c=7.4723(3) Å. We also report the observation of first order satellites in the B11 nuclear magnetic resonance, which indicated the presence of a nonzero quadrupole coupling frequency, νQ=276±3 kHz, and an asymmetry parameter η=0 at the boron atom sites. These values are in excellent agreement with electric-field-gradient (EFG) tensor calculations based on first principles. These calculations showed that the principal axis of the most negative EFG-tensor component, VZZ, is parallel to the c-axis of the crystal. This behavior is in agreement with the observed excess of B pz charge (c direction) over the px and py charges and is related to stronger metal-boron bonds compared to previously studied YB12 and LaB6, where the B–B bonds are stronger. Finally, the bonding properties of ReB2 are discussed in terms of densities of states, valence-electron densities, and partial charges.